Embodiments of the present inventive concept relate to an image sensor, and more particularly, to a method for compensating a pedestal level of an active signal generated from an output signal of an active pixel in an image sensor, and apparatuses performing the same.
An image sensor is a device for converting an optical image signal of detected light into an electrical image signal. Examples of image sensors include charge-coupled device (CCD) arrays and complementary metal oxide semiconductor (CMOS) arrays. In general, an image sensor may comprise an array of pixels each of which is configured to produce a pixel output signal representing an amount of light detected by the pixel. A pixel may employ a photosensitive device, such as a photodiode, to generate the output signal in response to received light. The image sensor may employ a detector to detect the pixel output signal produced by each pixel.
In general, an image sensor may employ a dark or black pedestal which adds a certain level to the output signal of each pixel for detection, for example to mask a noise level when little or no light is sensed by a pixel and insure that the detector does not try to detect negative levels due to temporal noise in the pixel in the absence of light. The image sensor determines the pedestal level to be added to the pixel output signal after performing an auto dark level compensation. When the auto dark level compensation operation is performed, a difference between a dark level of an active signal and a dark level of an optical black signal causes an offset of a pedestal level. In addition, the pedestal level varies according to an analog gain and an exposure time.